ip bandwidth-percent eigrp [as] [pct]
Configures the percentage of interface bandwidth that EIGRP can use for a specific autonomous system, limiting EIGRP traffic to prevent link saturation.
Definition: ip bandwidth-percent eigrp [as] [pct] is a Cisco IOS interface config command. Configures the percentage of interface bandwidth that EIGRP can use for a specific autonomous system, limiting EIGRP traffic to prevent link saturation.
Overview
The 'ip bandwidth-percent eigrp' command is a critical tool for controlling how much of an interface's bandwidth EIGRP is allowed to use for its control plane traffic. By default, EIGRP can consume up to 50% of the interface bandwidth for its packets (hello, update, query, reply, and acknowledgment). This default is designed to prevent EIGRP from starving user data traffic, but in some scenarios—such as low-speed links, satellite links, or links with strict QoS requirements—the default may be too high or too low.
This command allows a network engineer to override the default percentage for a specific EIGRP autonomous system (AS) on a per-interface basis. The command is entered in interface configuration mode and affects only EIGRP traffic for the specified AS on that interface. It does not affect other routing protocols or other EIGRP AS numbers.
The percentage is calculated based on the interface's configured bandwidth (set with the 'bandwidth' interface command). For example, if an interface has a bandwidth of 64 kbps and you set the EIGRP bandwidth percent to 25, EIGRP will be limited to 16 kbps. This command is particularly useful on serial links with low bandwidth, where EIGRP's default 50% could consume too much, or on high-speed links where you might want to allow EIGRP to use more than 50% to speed up convergence.
It is also used in conjunction with 'ip bandwidth-percent eigrp' to fine-tune EIGRP's behavior in complex topologies. The command is available in all IOS versions and is a standard part of EIGRP configuration. It does not require any special privilege level beyond the usual enable mode (privilege level 15).
The change takes effect immediately and is saved to the running configuration. There is no buffered output; the command either succeeds or fails with an error message. Understanding this command is essential for CCNA and CCNP candidates because it appears in both the exam topics and real-world network design.
It also ties into broader concepts like EIGRP metrics, load balancing, and QoS. When troubleshooting EIGRP performance issues, checking the bandwidth percent is often a first step. Alternatives include using 'ip bandwidth-percent eigrp' on the same interface for different AS numbers, or using 'ip eigrp bandwidth-percent' (a deprecated variant) but the standard is 'ip bandwidth-percent eigrp'.
This command is part of the EIGRP configuration workflow: after enabling EIGRP on an interface with 'network' or 'ip eigrp', you may adjust the bandwidth percent to control EIGRP's impact. It is also important to note that the bandwidth value used is the one configured on the interface, not the actual physical speed. Therefore, if the interface bandwidth is misconfigured, the EIGRP bandwidth percent will be calculated incorrectly.
This command is a simple but powerful way to ensure EIGRP does not overwhelm a link, especially in hub-and-spoke or DMVPN designs where many EIGRP neighbors may be exchanging updates over a single interface.
ip bandwidth-percent eigrp [as] [pct]When to Use This Command
- Limiting EIGRP bandwidth on a low-speed WAN link to avoid congestion with user traffic
- Controlling EIGRP overhead on a multi-access interface where multiple EIGRP processes run
- Preventing EIGRP from overwhelming a backup link during convergence events
- Adjusting bandwidth usage on a tunnel interface to match underlying physical constraints
Parameters
| Parameter | Syntax | Description |
|---|---|---|
| as | <1-65535> | The autonomous system number for the EIGRP process. This must match the AS number configured under the EIGRP router process. Common mistake: using the wrong AS number, which will cause the command to be accepted but have no effect on the intended EIGRP process. |
| pct | <1-999999> | The percentage of the interface bandwidth that EIGRP can use. Valid values are from 1 to 999999 (though values above 100 are rarely used). A value of 100 means EIGRP can use up to the full interface bandwidth. Common mistake: setting a very high percentage on a low-bandwidth link, which can cause EIGRP to consume all bandwidth and disrupt user traffic. |
Command Examples
Limit EIGRP AS 100 to 50% of interface bandwidth
ip bandwidth-percent eigrp 100 50R1(config-if)# ip bandwidth-percent eigrp 100 50
R1(config-if)# end
R1# show ip eigrp 100 interfaces
EIGRP-IPv4 Interfaces for AS(100)
Xmit Queue Mean Pacing Time Multicast Pending
Interface Peers Un/Reliable SRTT Un/Reliable Flow Timer Routes
Gi0/0 1 0/0 12 0/0 50 0
Bandwidth percent: 50
The command sets EIGRP AS 100 to use at most 50% of the interface bandwidth. The 'show ip eigrp interfaces' output confirms the setting under the interface line: 'Bandwidth percent: 50'.
Verify bandwidth percent on a serial link
show ip eigrp 100 interfaces serial 0/0/0EIGRP-IPv4 Interfaces for AS(100)
Xmit Queue Mean Pacing Time Multicast Pending
Interface Peers Un/Reliable SRTT Un/Reliable Flow Timer Routes
Se0/0/0 2 0/0 8 0/0 45 0
Bandwidth percent: 75
The output shows that on Serial0/0/0, EIGRP AS 100 is using 75% of the interface bandwidth. The 'Bandwidth percent' field indicates the configured limit.
Understanding the Output
The 'show ip eigrp interfaces' command displays per-interface EIGRP details. The 'Bandwidth percent' line shows the configured percentage of interface bandwidth that EIGRP may use. A value of 100 means full bandwidth, while lower values restrict EIGRP traffic.
If not configured, the default is 50% for low-speed interfaces (<= 1.544 Mbps) and 100% for others. Watch for values that are too low, causing EIGRP packet drops and neighbor flapping, or too high, starving other traffic. The 'Xmit Queue' and 'Mean SRTT' fields help assess congestion; high queues or SRTT may indicate bandwidth saturation.
Configuration Scenarios
Limit EIGRP bandwidth on a slow serial link
A branch office connects to headquarters via a 64 kbps serial link. The default EIGRP bandwidth percent of 50% would allow EIGRP to use up to 32 kbps, which is too much for the link. The goal is to limit EIGRP to 10% of the bandwidth to preserve capacity for user data.
Topology
R1(Serial0/0)---64kbps---(Serial0/0)R2Steps
- 1.Step 1: Enter global configuration mode: R1# configure terminal
- 2.Step 2: Enter interface configuration mode for the serial link: R1(config)# interface serial0/0
- 3.Step 3: Set the interface bandwidth to 64 kbps: R1(config-if)# bandwidth 64
- 4.Step 4: Limit EIGRP bandwidth to 10% for AS 100: R1(config-if)# ip bandwidth-percent eigrp 100 10
- 5.Step 5: Exit and verify: R1(config-if)# end
! interface Serial0/0 bandwidth 64 ip bandwidth-percent eigrp 100 10 !
Verify: Use 'show ip eigrp 100 interface serial0/0' to verify the bandwidth percent. Expected output includes 'Bandwidth percent: 10' and 'Bandwidth used: 6400 bits/sec' (10% of 64 kbps = 6.4 kbps).
Watch out: If the interface bandwidth is not set correctly (e.g., left at default 1544 kbps for serial), the percentage will be calculated on that incorrect value, leading to either too much or too little bandwidth allocated to EIGRP.
Increase EIGRP bandwidth usage on a high-speed link for faster convergence
A data center has a 1 Gbps Ethernet link between two core routers. The default 50% limit (500 Mbps) is sufficient, but the network engineer wants to allow EIGRP to use up to 80% of the bandwidth to speed up route propagation during convergence events.
Topology
R3(GigabitEthernet0/0)---1Gbps---(GigabitEthernet0/0)R4Steps
- 1.Step 1: Enter global configuration mode: R3# configure terminal
- 2.Step 2: Enter interface configuration mode: R3(config)# interface gigabitethernet0/0
- 3.Step 3: Set the bandwidth to 1000000 kbps (1 Gbps): R3(config-if)# bandwidth 1000000
- 4.Step 4: Increase EIGRP bandwidth percent to 80 for AS 200: R3(config-if)# ip bandwidth-percent eigrp 200 80
- 5.Step 5: Exit and verify: R3(config-if)# end
! interface GigabitEthernet0/0 bandwidth 1000000 ip bandwidth-percent eigrp 200 80 !
Verify: Use 'show ip eigrp 200 interface gigabitethernet0/0' to verify. Expected output includes 'Bandwidth percent: 80' and 'Bandwidth used: 800000000 bits/sec' (80% of 1 Gbps = 800 Mbps).
Watch out: Setting a percentage above 100 is allowed but can cause EIGRP to use more bandwidth than the interface can handle, leading to packet loss. Use values above 100 only if you have QoS mechanisms in place to prioritize EIGRP traffic.
Troubleshooting with This Command
When troubleshooting EIGRP performance issues, the 'ip bandwidth-percent eigrp' command is often a key factor. A healthy EIGRP neighbor relationship should show the bandwidth percent as configured, and the actual bandwidth used should be within that limit. To verify, use 'show ip eigrp interface [interface]' or 'show ip eigrp [as] interface [interface]'.
Look for the line 'Bandwidth percent: X' and 'Bandwidth used: Y bits/sec'. If the bandwidth used is consistently near the limit, EIGRP may be throttling its updates, which can slow convergence. If the bandwidth used is much lower than the limit, it may indicate that EIGRP is not sending many updates (which is normal in a stable network) or that there is a problem with the neighbor relationship.
Common symptoms that this command helps diagnose include: (1) EIGRP neighbors flapping due to excessive packet loss when EIGRP traffic exceeds the link capacity; (2) Slow convergence because EIGRP is artificially limited to a very low percentage; (3) High CPU utilization on the router because EIGRP is sending too many packets. To diagnose, first check the interface bandwidth with 'show interface' to ensure it matches the actual link speed. Then check the EIGRP bandwidth percent with 'show ip eigrp interface'.
If the percent is too low, increase it. If EIGRP is causing link saturation, decrease the percent. Also correlate with 'show ip eigrp traffic' to see the volume of EIGRP packets.
If the 'Hello' count is high, it may indicate a problem with hello timers or neighbor loss. Use 'debug eigrp packets' cautiously to see the actual packet flow, but be aware that debug can be CPU-intensive. Another useful command is 'show ip eigrp topology' to see if routes are missing due to bandwidth throttling.
In summary, the bandwidth percent command is a simple but powerful tool to control EIGRP's impact on the network. Always verify the interface bandwidth first, as it is the foundation for the percentage calculation. If you see unexpected behavior, check both the configured percent and the actual bandwidth used.
Remember that the command affects only the specified AS, so if you have multiple EIGRP processes, you need to configure each one separately. Also note that the command does not affect EIGRPv6 (IPv6) — for IPv6, use 'ipv6 bandwidth-percent eigrp'.
CCNA Exam Tips
Remember the default bandwidth percent: 50% for links <= 1.544 Mbps, 100% for faster links
The command is configured under interface configuration mode, not router eigrp mode
EIGRP uses bandwidth percent to throttle hello and update packets; setting too low can cause neighbor loss
On serial interfaces with low bandwidth, always verify the bandwidth command is set correctly before adjusting percent
Common Mistakes
Forgetting to set the interface bandwidth with 'bandwidth' command before adjusting percent, leading to incorrect calculations
Applying the command to the wrong EIGRP AS number, causing no effect on the intended process
Setting the percent too low (e.g., 1%) causing EIGRP neighbor relationships to fail due to packet drops
ip bandwidth-percent eigrp [as] [pct] vs bandwidth [kbps]
Both commands operate in interface configuration mode and relate to bandwidth, but they serve different purposes: the bandwidth command sets the interface's bandwidth value for routing protocol metrics, while ip bandwidth-percent eigrp limits the percentage of that bandwidth EIGRP can use. They are often confused because changing one can affect EIGRP behavior indirectly.
| Aspect | ip bandwidth-percent eigrp [as] [pct] | bandwidth [kbps] |
|---|---|---|
| Scope | EIGRP-specific (per AS) | All routing protocols and QoS |
| Configuration mode | Interface configuration | Interface configuration |
| Persistence | Affects EIGRP traffic only | Affects all protocols and QoS |
| Precedence | Overrides default EIGRP bandwidth use of 50% | Sets base bandwidth for EIGRP percent calculation |
| Typical use | Limit EIGRP traffic on congested links | Adjust metric calculation for non-standard link speeds |
Use ip bandwidth-percent eigrp [as] [pct] when you need to control the maximum percentage of interface bandwidth that EIGRP can consume for a specific autonomous system, typically to prevent EIGRP from saturating a slow or variable-bandwidth link.
Use bandwidth [kbps] when you need to set the interface bandwidth for routing protocol metric calculations (e.g., EIGRP, OSPF) to reflect actual link capacity, overriding the default detected value.
Platform Notes
In IOS-XE (e.g., 16.x), the command syntax is identical to classic IOS: 'ip bandwidth-percent eigrp [as] [pct]'. The output of 'show ip eigrp interface' is also similar, though some fields may be rearranged. In NX-OS (Cisco Nexus switches), the equivalent command is 'ip bandwidth-percent eigrp [as] [pct]' under interface configuration mode, but note that NX-OS uses a different EIGRP implementation and the command may have slightly different behavior.
For example, NX-OS does not support the 'bandwidth' interface command for all interface types; instead, it uses the actual link speed. Also, NX-OS requires the 'feature eigrp' command to enable EIGRP. On Cisco ASA firewalls, EIGRP is not supported, so this command does not apply.
In IOS-XR, the command is 'bandwidth-percent eigrp [as] [pct]' under interface configuration, but IOS-XR uses a different configuration hierarchy (e.g., 'router eigrp [as]' then 'interface [type]' then 'bandwidth-percent [pct]'). There is no significant difference between IOS 12.x and 15.x for this command, but in 16.x (IOS-XE), the output formatting may be slightly different. Always check the specific platform documentation for exact syntax.
For example, on some older IOS versions, the command was 'ip eigrp bandwidth-percent' (deprecated), but the current standard is 'ip bandwidth-percent eigrp'.
Related Commands
bandwidth [kbps]
Sets the bandwidth value (in kbps) on an interface for routing protocol metric calculations and QoS, overriding the default detected bandwidth.
show ip eigrp interfaces
Displays detailed information about interfaces on which EIGRP is enabled, including neighbor status, pending routes, and interface statistics, used to verify EIGRP adjacency and interface participation.
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